The invention relates to a device for swinging the lifting arms of a container and trailer-handling combination yoke device upwards, and transfer thereof to a position inside the perimeter of an imaginary rectangular figure resulting from drawing imaginary lines joining the laterally outer ends of respective the long sides of the yoke means of the device, when containers and trailers are being handled. Such a location of the lifting arms of the combination yoke device inside the long sides of the yoke means is of the greatest importance when using the yoke means for handling containers, during which the yoke means supports the container at each of the four corners of the top of the container by means of so-called twist locks, especially in the case when a close arrangement of containers in, for example cargo terminals is desired for space reasons, which has, of course, great economic advantages.
A device of this type is already known. In the known device, the lifting arms are first swung upwards by means of a conventional hydraulic cylinder, the piston rod of which is attached to the lifting arm and the cylinder of which is attached to an intermediate piece in which the arm is pivotably suspended, to a substantially horizontal position, after which the intermediate piece, with the upwardly swung arm and the hydraulic cylinder, is pulled-in to a position inside the long side of the yoke means, by means of another conventional hydraulic cylinder arranged on a stationary transverse beam included in the frame in which a movable beam is arranged telescopically, said intermediate piece being attached to said movable beam.
A disadvantage of this known device is that the lifting arms in an upwardly swung, pulled-in position will not remain in this position due to the fact that the hydraulic cylinders has a tendency to leak of hydraulic liquid, allowing the arms to sink from their horizontal position.
This sinking which, moreover, is accelerated by the violent movements of the yoke means in handling and, of course, may be as great for different arms, may result in the lifting arms getting in contact with one another and sometimes, moreover, to hook to and lock each other and, which is very common, the lifting arms knocking a hole in the container or the trailer which, for example, in a following rain may have devastating effects on the contents of the container or trailer. Such damage to the container or trailer must be repaired immediately-resulting in a stoppage of the handling work which, consequently, involves losses of both time and money.
Another disadvantage is the bad moderation of the swinging movements of the lifting arms in the longitudinal direction of the yoke means, for example due to an unevenly distributed load in the container or inexact operation of the yoke means caused by the conventional single piston-type hydraulic cylinders of the lifting arms in handling which may result in a displacement of the load, damage to the load in the case of a fragile load or to the very yoke means, trailer and container.